score:3
Rome2Rio.com is great for searching for this sort of thing. The train station in Charleroi is a little south of the airport, so you'll probably have to take a bus or taxi to the train, but there's a good rail connection between the two cities. According to Rome2Rio, the bus and train will cost you under $50 USD (you can change currencies on the website through one of the settings).
Upvote:3
A stated by ColeS you can take the train. It's convenient and confortable. You will have to take the bus from the airport to the train station.
You can even travel cheaper though. The Charleroi has a special ticket that combines train and bus. It's fixed price for any place in Belgium and costs 19,10Euro.